U.S. patent number 4,314,855 [Application Number 06/104,379] was granted by the patent office on 1982-02-09 for method of cleaning test probes.
This patent grant is currently assigned to Bell Telephone Laboratories, Incorporated. Invention is credited to Chuan C. Chang, Jitendra Kumar.
United States Patent |
4,314,855 |
Chang , et al. |
February 9, 1982 |
Method of cleaning test probes
Abstract
Contaminants that accumulate on test probes utilized to contact
aluminum pads on integrated circuit chips cause the probe
resistance to become unacceptably high. As disclosed herein, the
contaminants (predominantly a mixture of aluminum and aluminum
oxide) are substantially removed by immersing the probes in boiling
water. Adding small quantities of phosphoric and/or hydrofluoric
acids to the water further improves the cleaning action.
Inventors: |
Chang; Chuan C. (Berkeley
Heights, NJ), Kumar; Jitendra (Bridgewater, NJ) |
Assignee: |
Bell Telephone Laboratories,
Incorporated (Murray Hill, NJ)
|
Family
ID: |
22300193 |
Appl.
No.: |
06/104,379 |
Filed: |
December 17, 1979 |
Current U.S.
Class: |
134/3; 134/26;
134/35; 134/41; 134/6; 451/54 |
Current CPC
Class: |
B08B
3/10 (20130101); B08B 3/08 (20130101) |
Current International
Class: |
B08B
3/08 (20060101); B08B 3/10 (20060101); B08B
003/08 (); B08B 003/10 () |
Field of
Search: |
;134/3,41,6,7,26,28,35,42 ;51/323 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caroff; Marc L.
Attorney, Agent or Firm: Canepa; Lucian C.
Claims
We claim:
1. In a method of removing contaminants from electrically
conductive test probes that are utilized to contact aluminum pad
regions on an integrated circuit chip, the improvement comprising
the step of cleaning said probes after multiple such contacts by
immersing the probes in boiling water to remove contaminants
accumulated during contacting of said aluminum pad regions.
2. A method as in claim 1 wherein said water is deionized and said
cleaning step is carried out for about 10 minutes.
3. A method as in claim 2 wherein said cleaning step is carried out
in a solution that comprises said water to which 0.1% by volume
phosphoric acid and/or 0.1% by volume hydrofluoric acid have been
added.
4. In a method of removing contaminants from electrically
conductive test probes that are utilized to contact aluminum pad
regions on an integrated circuit chip, the improvement comprising
the step of cleaning said probes after multiple such contacts by
alternately abrading the probes and immersing them in boiling water
to remove contaminants accumulated during contacting of said
aluminum pad regions.
5. In a method of removing contaminants from electrically
conductive test probes that are utilized to contact aluminum pad
regions on an integrated circuit chip, the improvement comprising
the step of cleaning said probes after multiple contacts of said
aluminum pad regions by immersing the probes in a bath consisting
only of boiling water.
Description
BACKGROUND OF THE INVENTION
This invention relates to a cleaning procedure and, more
specifically, to a method of cleaning test probes that are utilized
for contacting conductive pads on electronic devices such as
integrated circuit chips.
Integrated circuit chips formed on a wafer may each include
multiple contact pads. One known technique for testing such
integrated circuits utilizes an array of conductive probes mounted
in a base member. Such an assembly is commonly called a probe card.
The probes are configured to correspond exactly to the arrangement
of pads on each chip. In the probe card, electrical connections
respectively extend between the probes and terminals to be
connected to associated testing equipment. By bringing the probes
into electrical contact with the pads, the circuitry embodied in
each chip is connected to the associated equipment for testing.
Heretofore, during the course of successively probing integrated
circuit chips of the type having aluminum contact pads, it has been
observed in practice that the resistance between the probes and the
pads becomes in time unacceptably high. This is particularly true
if the testing procedure is specified to be carried out at an
elevated temperature, say, 85 degrees C.
A typical expedient resorted to for maintaining the probe-to-pad
resistance at acceptable levels is to periodically abrade the probe
tips against a rough material such as a ceramic or ground glass
surface. However, complete reliance on abrasion as a cleaning
technique has some disadvantages. For example, exactly reproducible
abrasive procedures are difficult to devise. Also, abrading may
degrade the planarity of the probe array and, further, may in time
mechanically damage the probe tips to the point where they are
unusable. In addition, contaminants scraped from the probe tips
during abrasion may end up on the shanks of the probes. Moreover,
insulating particles from the abrasive surface may adhere to the
probes during the cleaning operation. In turn, these contaminants
and particles may later become interposed between the probes and
the contact pads thereby preventing the establishment of
low-resistance paths therebetween.
Another known expedient for cleaning probes involves the use of an
etchant solution containing sodium hydroxide. Such an etchant is,
however, undesireable because it is highly corrosive. Moreover,
sodium is recognized to be one of the worst contaminants for
electronic devices and especially for integrated circuits.
Final electrical testing is performed on finished devices in which
considerable processing effort has been invested. Even a slight
degradation in probe performance can provide incorrect test
results. As a consequence, devices that are actually satisfactory
may be discarded as being faulty. The economic cost of such
erroneous testing is apparent and can be substantial.
In view of the above, efforts have been directed at trying to
devise a simple alternative procedure for cleaning test probes
utilized to contact aluminum pads on integrated circuit chips. It
was recognized that such efforts, if successful, would provide an
improved cleaning procedure that would lead to more reliable
testing of electronic devices with an attendant reduction in the
overall cost of the devices.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is an improved
procedure for cleaning probes.
Briefly, this and other objects of the present invention are
realized in a specific illustrative technique for cleaning test
probes that are utilized to contact aluminum pads on integrated
circuit chips. The basic cleaning procedure comprises simply
immersing the probes in boiling water. To further enhance the
cleaning action, it has been found generally advantageous to add
small quantities of phosphoric and/or hydrofluoric acids to the
water. In a modification of the basic procedure, abrading and
boiling are alternated to effect cleaning of the probes.
DETAILED DESCRIPTION
The first step in testing an integrated circuit wafer containing
multiple chips is to connect each chip to an associated test
system. This is typically accomplished by means of a standard probe
card assembly that comprises tiny metal probes that are designed to
be respectively placed in contact with conductive pads on each
chip. Illustratively, the probes, made, for example, of tungsten
wire, taper to about 0.025 millimeters at their ends. The probes
are mounted on a printed circuit board that is adapted to be held
in a fixed position above a test pedestal which positions the wafer
underneath the probes, as is well known in the art (see, for
example, "Integrated Circuit Testing," by M. R. Barber and A.
Zacharias, Bell Laboratories Record, pages 125-130, May 1977).
Herein, for purposes of a specific illustrative example, the probes
will be assumed to be made of tungsten. But it should be realized
that the principles of the present invention are also applicable to
the cleaning of standard test probes made of other materials such
as, for example, palladium or copper-beryllium alloys, or
gold-plated or rhodium-plated probes.
The principles of the present invention are directed to cleaning
test probes that are utilized to establish electrical connections
to aluminum contact pads on integrated circuit chips to be tested.
In one particular illustrative case, a wafer included 100 chips
each comprising a large-scale-integrated microprocessor circuit to
be tested. Each chip included 40 aluminum contact pads disposed
around the periphery thereof. Testing of the circuits was specified
to be done at 85 degrees C.
In practice, without a suitable cleaning procedure for the
herein-considered test probe assembly, the probe-to-pad contact
resistance of one or more probes becomes unacceptably high after
testing about 20 wafers at 85 degrees C. This increase in contact
resistance is typically less severe if testing is conducted at room
temperature.
Optical investigation of the probes indicated that material becomes
attached thereto during lowering of the probes (when the probe tips
slide forward after impacting the contact pads) and again during
lifting of the probes (when the tips slide backwards). The precise
details of how these successive contacting events result in the
formation of resistive material on the probes is complex and not
entirely understood.
Auger electron spectroscopic analysis of probes indicated that the
contaminant material accumulated thereon during testing was
predominantly a mixture of elemental aluminum, aluminum oxide and
aluminum oxyfluoride. In addition, the accumulated material was
determined to include relatively small quantities of oxygen,
carbon, silicon, nitrogen, sodium and magnesium compounds.
In accordance with the principles of this invention, applicants
discovered that, surprisingly, contaminated test probes of the type
specified above could be effectively cleaned simply by immersing
them in boiling water. Deionized water is preferred in practice
because it is a relatively standard and well characterized
substance, but ordinary tap water is usually satisfactory also.
Illustratively, the entire probe assembly is boiled in water for
approximately 10 minutes. After being dried, probe assemblies
cleaned in this manner are substantially devoid of the previously
specified contaminant materials and exhibit excellent probe-to-pad
contact resistance properties.
Under actual testing conditions, it is advantageous to clean the
aforespecified probes in the manner set forth above after probing a
maximum of 20 wafers at 85 degrees C. or after probing a maximum of
100 wafers at room temperature.
A complete and definitive theory of the mechanism involved in the
aforespecified cleaning action has not been formulated.
Nevertheless, a tentative explanation of the mechanism has been
postulated by the applicants. Although the validity and scope of
the present invention are not dependent on that explanation, it is
instructive to set it forth. The primary mechanism for contaminant
removal is probably oxidation of elemental aluminum and hydration
of aluminum oxide. The hydrated complexes apparently dissolve
readily in hot water (in the sense that they can migrate away from
the location where they were formed), and the natural agitation of
boiling water is almost certainly helpful in facilitating movement
of such complexes. In the course of their physical movement, the
hydrated complexes of aluminum carry with them or dislodge other
contaminants.
Furthermore, applicants have determined that adding relatively
small quantities of phosphoric and/or hydrofluoric acids to the
aforespecified water bath enhances the cleaning action thereof. In
particular, phosphoric acid accelerates the dissolution rates of
aluminum and its oxides, and hydrofluoric acid aids in the removal
of silicon dioxide and silicon nitride from the test probes. (Both
acids have such low vapor pressure at 100 degrees C. that they are
not significantly depleted by evaporation from the water.) In
accordance with a specific feature of the principles of the present
invention, one particularly advantageous solution for cleaning test
probes included water having 0.1% by volume phosphoric acid and/or
0.1% by volume hydrofluoric acid. When hydrofluoric acid is
utilized, the vessel holding the cleaning solution is
advantageously lined with an acid-resistant material such as Teflon
synthetic resin polymer. (Teflon is a registered trademark of E. I.
DuPont de Nemours and Co.)
Finally, it is to be understood that the above-described procedures
are only illustrative of the principles of the present invention.
In accordance with these principles, numerous modifications and
alternatives may be devised by those skilled in the art without
departing from the spirit and scope of the invention. For example,
it is sometimes advantageous to combine the herein-described water
boiling technique with some degree of abrasion. One illustrative
such combination comprises the following cleaning sequence: test 20
wafers, abrade, test 20 wafers, abrade, test 20 wafers, boil as
specified hereinabove, . . . (repeat sequence). The precise number
of abradings between boilings is determined by the particular
operating test conditions such as the degree of aluminum
contamination, temperature, humidity, et cetera. This combined
procedure has the advantage of longer intervals between boilings,
allows some use of simple abrading techniques, and avoids the
eventual build-up on the probes of material that cannot be boiled
off.
Moreover, in those cases wherein the cleaning of many probe cards
is required, it is advantageous to construct an assembly to hold a
number of cards in the water bath simultaneously.
* * * * *